1. Field of the Invention
The present invention relates to a robot gripping device which grips a workpiece which may be of various shapes and may be arranged in various orientations.
2. Description of the Related Art
The front end of a wrist of a robot is provided with a gripping device for gripping a workpiece. FIG. 10A and FIG. 10B are a top view and a side view of a first hand in the related art. FIG. 10A and FIG. 10B show a servo hand which is attached to a robot. Such a servo hand has a structure similar to a human hand and is advantageous for gripping various shapes and various orientations of workpieces
However, the servo hand which is shown in FIG. 10A and FIG. 10B has a plurality of servo motors and a complicated link mechanism built into it. Therefore, such a servo hand is extremely expensive and requires fine, complicated control. For this reason, at the present, the spread of such servo hands has been slow.
Further, FIG. 11 is a view which shows a second hand in the related art. A chuck which is shown in FIG. 11 is provided with two or three finger parts. However, the chuck which is shown in FIG. 11 usually has no versatility and can only grip predetermined shapes of workpieces. When gripping a complicated shape of workpiece, the workpiece had to be arranged in a limited, specific orientation.
Furthermore, Japanese Patent Publication No. 2011-245566A discloses a gripping device which uses bent plate-shaped members to open and close a gripping part. U.S. Pat. No. 3,527,492 discloses a gripping device where a finger part is comprised of an outside spring finger and an inside flexible finger.
However, the gripping device of Japanese Patent Publication No. 2011-245566A cannot open the finger parts wide, so can only grip small sized workpieces. Further, there was the problem that the drive part of the gripping device was considerably large compared with the gripping part.
Furthermore, the spring finger and flexible finger of U.S. Pat. No. 3,527,492 are made of plate springs with low rigidity. Therefore, the gripping device of U.S. Pat. No. 3,527,492 can only grip a light weight workpiece. Further, when gripping, a large force is required for bending the outside spring finger, so the gripping device of U.S. Pat. No. 3,527,492 is low in drive efficiency. Furthermore, the outside spring finger bends outward at the time of gripping, so there is the problem that the spring finger easily contacts nearby objects.
In this regard, a gripping device which is attached to a front end of a wrist of a robot is also used when taking out workpieces which are randomly stacked in a holding box. In such a case, high a gripping precision is not required in the sense of the relative positional relationship between the hand and the workpiece when the hand of the gripping device grips a workpiece. Even if the gripping precision is low, for example, if the hand roughly grabs a part, it is sufficient that the hand can reliably grip the workpiece and take it outside of the holding box.
However, in the gripping device such as shown in FIG. 10 or FIG. 11, it is only possible to grip a workpiece which is arranged at a predetermined orientation. Further, to keep the gripping device from striking the inside wall of the holding box, it is necessary to make the gripping device face downward. For this reason, it is not possible to grip a workpiece which is positioned at a corner of the holding box. Furthermore, in the related art, it was not possible to confirm whether the gripping device had indeed gripped a workpiece.
The present invention was made in consideration of such a situation and has as its object the provision of a robot gripping device with a high versatility which can approach a workpiece vertically downward and grip it with a high reliability without regard as to the orientation and shape of the workpiece and without using an expensive servo hand.